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Greenhouse
Gases
Many chemical compounds found in the Earths atmosphere act as greenhouse gases. These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earths surface, some of it is reflected back towards
space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere. Over time, the amount of energy sent from the sun to the Earths surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earths surface roughly constant. Many gases exhibit these greenhouse properties. Some of them occur in nature (water vapor, carbon dioxide, methane, and nitrous oxide), while others are exclusively human-made (like gases used for aerosols).
Greenhouse gases naturally blanket the Earth and keep it about 33 degrees
Celsius warmer than it would be without these gases in the atmosphere. This is
called the Greenhouse Effect. Over the past century, the Earth has increased
in temperature by about .5 degrees Celsius and many scientists believe this is
because of an increase in concentration of the main greenhouse gases: carbon
dioxide, methane, nitrous oxide, and fluorocarbons. People are now calling this
climate change over the past century the beginning of Global
Warming. Fears
are that if people keep producing such gases at increasing rates, the results
will be negative in nature, such as more severe floods and droughts, increasing
prevalence of insects, sea levels rising, and Earth's precipitation may be
redistributed. These changes to the environment will most likely cause
negative effects on society, such as lower health and decreasing economic
development. However, some scientists argue that the global warming we are
experiencing now is a natural phenomenon, and is part of Earth's natural cycle.
Presently, nobody can prove if either theory is correct, but one thing is
certain; the world has been emitting greenhouse gases at extremely high rates
and has shown only small signs of reducing emissions until the last few years.
After the 1997 Kyoto Protocol, the world has finally taken the first step in
reducing emissions.
The Greenhouse Effect
The "greenhouse effect" is the heating of the Earth due to the presence of greenhouse gases. It is named this way because of a similar effect produced by
the glass panes of a greenhouse. Shorter-wavelength solar radiation from the
sun passes through Earth's atmosphere, then is absorbed by the surface of the
Earth, causing it to warm. Part of the absorbed energy is then reradiated back
to the atmosphere as long wave infrared radiation. Little of this long wave
radiation escapes back into space; the radiation cannot pass through the
greenhouse gases in the atmosphere. The greenhouse gases selectively transmit
the infrared waves, trapping some and allowing some to pass through into
space. The greenhouse gases absorb these waves and reemits the waves downward, causing
the lower atmosphere to warm.
Greenhouse Gases
The main greenhouse gases are:
Carbon Dioxide,
Methane,
Nitrous Oxide,
Fluorocarbons
Atmospheric Levels of greenhouse gases is Increasing
Levels of several important greenhouse gases have increased by about 25 percent since large-scale industrialization began around 150 years ago
During the past 20 years, about three-quarters of human-made carbon dioxide emissions were from burning fossil fuels.
Trends in Atmospheric Concentrations and Anthropogenic Emissions of Carbon Dioxide
Concentrations of carbon dioxide in the atmosphere are naturally regulated by numerous processes collectively known as the
carbon cycle.
The movement of carbon between the atmosphere and the land and oceans is dominated by natural processes, such as plant photosynthesis. While these natural processes can absorb some of the net 6.1 billion metric tons of anthropogenic carbon dioxide emissions produced each year (measured in carbon equivalent terms), an estimated 3.2 billion metric tons is added to the atmosphere annually. The Earths positive imbalance between emissions and absorption results in the continuing growth in greenhouse gases in the atmosphere.
The Effect of
Greenhouse Gases have on Climate Change
Naturally, if there are more greenhouse gases in the atmosphere, this
greenhouse effect will be more significant and raise the temperature of Earth
more than if humans didn't emit as much greenhouse gases. Given the natural variability of the Earths climate, it is difficult to determine the extent of change that humans cause. In computer-based models, rising concentrations of greenhouse gases generally produce an increase in the average temperature of the Earth. Rising temperatures may, in turn, produce changes in weather, sea levels, and land use patterns, commonly referred to as climate
change.
Assessments generally suggest that the Earth's climate has warmed over the past century and that human activity affecting the atmosphere is likely an important driving factor. A National Research Council study dated May 2001
stated, Greenhouse gases are accumulating in Earths atmosphere as a result of human activities, causing surface air temperatures and sub-surface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.
However, there is uncertainty in how the climate system varies naturally and reacts to emissions of
greenhouse gases. Making progress in reducing uncertainties in projections of future climate will require better awareness and understanding of the buildup of greenhouse gases in the atmosphere and the behavior of the climate system.
The Sources of Greenhouse Gases In the U.S., our greenhouse gas emissions come mostly from energy use. These are driven largely by economic growth, fuel used for electricity
generation, and weather patterns affecting heating and cooling needs. Energy-related carbon dioxide emissions, resulting from petroleum and natural gas, represent 82 percent of total U.S. human-made greenhouse gas emissions. The connection between energy use and carbon dioxide emissions is explored in the box on the reverse side .
Another greenhouse gas, methane, comes from landfills, coal mines, oil and gas operations, and agriculture; it represents 9 percent of total emissions. Nitrous oxide (5 percent of total emissions), meanwhile, is emitted from burning fossil fuels and through the use of certain fertilizers and industrial processes. Human-made gases (2 percent of total emissions) are released as byproducts of industrial processes and through leakage.
Effects of Global Warming on Society
Agriculturally, Dr. Sylvan H. Wittwer believes that global warming is good for the human race, because it helps increase food production. "The most
determinant factor in agriculture production is climate. History reveals that
for food production, warming is better than cooling." Dr. Wittwer says that
carbon dioxide is an essential nutrient for the production of food, and food is
one of the most important things in our lives. As the temperature rises, more
farmland will be open towards the poles and the length of the growing season
will also lengthen. With all the people who go hungry each day, Dr. Wittwer
believes food production should be one of our main concerns. Dr. Wittwer is the
scientific pioneer who conducted the original studies on atmospheric CO2
enhancement of the production of food crops. Increasing amounts of greenhouse gases in the atmosphere and global warming
could also lead to more health concerns. A statement released from the
Intergovernmental Panel on Climate Change (IPCC) said, "Climate change is likely
to have wide-ranging and mostly adverse impacts on human health, with
significant loss of life." As temperatures increase towards the poles, similar
to farmland, insects and other pests migrate towards Earth's poles. These
insects and pests could be allowed to migrate up to 550 Km or 550 miles. Some
insects carry diseases such as malaria and dengue fever. Thus, an increase in
these particular insects and pests closer to the poles results in an increase in
these diseases. This could lead to 50 to 80 million additional cases of Malaria
annually, a 10-15% increase. "Malaria and dengue fever are already beginning to
spread pole wards", said Jane Lubchenco, past president of American Association
for the advancement of science.
The Prospect for Future Emissions
World carbon dioxide emissions are expected to increase by 1.9 percent annually between 2001 and 2025 Much of the increase in these emissions is expected to occur in the developing world where emerging economies, such as China and India, fuel economic development with fossil energy. Developing countries
emissions are expected to grow above the world average at 2.7 percent annually between 2001 and 2025; and surpass emissions of industrialized countries near 2018.
The U.S. produces about 25 percent of global carbon dioxide emissions from burning fossil fuels; primarily because our economy is the largest in the world and we meet 85 percent of our energy needs through burning fossil fuels. The U.S. is projected to lower its carbon intensity by 25 percent from 2001 to 2025, and remain below the world average.
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